A biomarker is a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention, Atkinson et al, Clin. Pharmacol. Ther., 69: 89-95 (2001). Biomarkers vary widely in nature, ease of measurement, and correlation with physiological states of interest, e.g. Frank et al, Nature Reviews Drug Discovery, 2: 566-580 (2003). It is widely believed that the development of new validated biomarkers will lead both to significant reductions in healthcare and drug development costs and to significant improvements in treatment for a wide variety of diseases and conditions. Thus, a great deal of effort has been directed to using new technologies to find new classes of biomarkers, e.g. Petricoin et al, Nature Reviews Drug Discovery, 1: 683-695 (2002); Sidransky, Nature Reviews Cancer, 2: 210-219 (2002).
The interactions of cell surface membrane components play crucial roles in transmitting extracellular signals to a cell in normal physiology, and in disease conditions. In particular, many types of cell surface receptors undergo dimerization, oligomerization, or clustering in connection with the transduction of an extracellular event or signal, e.g. ligand-receptor binding, into a cellular response, such as proliferation, increased or decreased gene expression, or the like, e.g. George et al, Nature Reviews Drug Discovery, 1: 808-820 (2002); Mellado et al, Ann. Rev. Immunol., 19: 397-421 (2001); Schlessinger, Cell, 103: 211-225 (2000); Yarden, Eur. J. Cancer, 37: S3-S8 (2001). The role of such signal transduction events in diseases, such as cancer, has been the object of intense research and has led to the development of several new drugs and drug candidates, e.g. Herbst and Shin, Cancer, 94: 1593-1611 (2002); Yarden and Sliwkowski, Nature Reviews Molecular Cell Biology, 2: 127-137 (2001); McCormick, Trends in Cell Biology, 9: 53-56 (1999); Blume-Jensen and Hunter, Nature, 411: 355-365 (2001).
Expression levels of individual cell surface receptors have been used successfully as biomarkers, e.g. Slamon et al, U.S. Pat. No. 4,968,603 (Her2 expression). However, individual receptor expression level alone is not always a reliable indicator of a disease status or condition, e.g. Chow et al, Clin. Cancer Res., 7: 1957-1962 (2001) (EGFR, or Her1, expression). Despite the important role that receptor dimerization plays in cellular and disease processes, receptor dimer expression has not been employed as a biomarker, in part due to the inconvenience and lack of sensitivity of current measurement technologies and the inability or impracticality of using such technologies to carry out measurements on patient samples, which may be formalin fixed and/or in too small a quantity for analysis, e.g. Price et al, Methods in Molecular Biology, 218: 255-267 (2003); Stagljar, Science STKE 2003, pe56 (2003); Koll et al, International patent publication WO 2004/008099; Golemis, editor, Protein-Protein Interactions (Cold Spring Harbor Laboratory Press, New York, 2002); Sorkin et al, Curr. Biol., 10: 1395-1398 (2000); McVey et al, J. Biol. Chem., 17: 14092-14099 (2001); Salim et al, J. Biol. Chem., 277: 15482-15485 (2002); Angers et al, Annu. Rev. Pharmacol. Toxicol., 42: 409-435 (2002); Szollosi et al, Reviews in Molecular Biotechnology, 82: 251-266 (2002); Matko et al, Meth. in Enzymol., 278: 444-462 (1997); Reed-Gitomer, U.S. Pat. No. 5,192,660.
In view of the above, the availability of a new class of biomarkers in patient samples based on the presence, absence, and/or profile or ratios of cell surface receptor dimers or complexes involved with key intracellular processes, such as signal transduction, would advance the field of medicine by providing a new tool for diagnosis, prognosis, patient stratification, and drug development.